U.S. patent application number 12/884705 was filed with the patent office on 2011-10-06 for bidirectional 3 phase power meter for compensating reverse load flow and method for metering thereby.
This patent application is currently assigned to KOREA ELECTRIC POWER CORPORATION. Invention is credited to Dong-Yeol Shin.
Application Number | 20110241655 12/884705 |
Document ID | / |
Family ID | 43513414 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110241655 |
Kind Code |
A1 |
Shin; Dong-Yeol |
October 6, 2011 |
BIDIRECTIONAL 3 PHASE POWER METER FOR COMPENSATING REVERSE LOAD
FLOW AND METHOD FOR METERING THEREBY
Abstract
The present invention relates to a bidirectional 3 phase power
meter for compensating reverse load flow and a method for metering
thereby. According to the present invention, there is provided a
bidirectional 3 phase power meter for compensating reverse load
flow which allows calculating power receiving and power
transmitting apparent power and power factor using the detected
voltage/current and a method for metering thereby.
Inventors: |
Shin; Dong-Yeol; (Daejeon,
KR) |
Assignee: |
KOREA ELECTRIC POWER
CORPORATION
Seoul
KR
|
Family ID: |
43513414 |
Appl. No.: |
12/884705 |
Filed: |
September 17, 2010 |
Current U.S.
Class: |
324/140R |
Current CPC
Class: |
G01R 21/1331
20130101 |
Class at
Publication: |
324/140.R |
International
Class: |
G01R 19/10 20060101
G01R019/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2010 |
KR |
10-2010-0030568 |
Claims
1. A bidirectional 3 phase power meter for compensating reverse
load flow comprising: a voltage/current detecting unit detecting a
voltage per phase or current per phase; a bidirectional measuring
unit measuring power receiving direction or power transmitting
direction by calculating phase difference per phase using the
voltage per phase or current per phase value and calculating
neutral line current; an instantaneous power calculating unit
calculating instantaneous power by using the voltage per phase or
current per phase and the phase difference per phase; a reverse
load flow determining unit determining occurrence of reverse load
flow through the phase difference per phase and the neutral line
current calculated from the bidirectional measuring unit; a reverse
load flow calculating unit calculating reverse load flow power
generated when the reverse load flow determining unit determines
occurrence of reverse load flow; an actual power usage calculating
unit calculating actual power usage by calculating instantaneous
compensation power per phase and 3 phase instantaneous compensation
power using the instantaneous power and the reverse load flow
power; a power transmitting/receiving direction determining unit
determining active power or reactive power of the actual power
usage; a power meter value storing unit compensating the amount of
active power and reactive power calculated from the power
transmitting/receiving direction determining unit and accumulating
and storing the result; and an apparent power/power factor
calculating unit calculating apparent power and power factor using
the active power and reactive power stored at the power meter value
storing unit and the amount of accumulated power.
2. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 1, wherein the bidirectional measuring unit
further comprises a power receiving direction measuring unit; and a
power transmitting direction measuring unit, in which the power
receiving direction measuring unit determines phase by subtracting
the phase of the current per phase from the phase of the voltage
per phase and the power transmitting direction measuring unit
determines phase by adding 180.degree. to the phase determined at
the power receiving direction measuring unit.
3. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 2, wherein the bidirectional measuring unit
further comprises a neutral line current measuring unit determining
the neutral line current by calculating 3 phase current vector
SUM.
4. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 1, wherein the instantaneous power calculating
unit further comprises a power receiving instantaneous power
calculating unit calculating power receiving direction
instantaneous power; and a power transmitting instantaneous power
calculating unit calculating power transmitting direction
instantaneous power.
5. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 4, wherein the power receiving instantaneous
power calculating unit further comprises an instantaneous active
power calculating unit calculating instantaneous active power per
phase; and an instantaneous reactive power calculating unit
calculating instantaneous reactive power per phase.
6. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 1, wherein the reverse load flow determining
unit further comprises: a negative-sequence selecting unit
selecting a negative-sequence based on a smaller value from a
positive-sequence and a negative-sequence; a current intensity
comparing unit outputting 0 or 1 by comparing a negative-sequence
intensity outputted from the negative-sequence selecting unit with
a zero-sequence intensity; a plurality of voltage phase difference
comparing units outputting 0 or 1 by comparing phase difference of
voltages per phase; a first AND gate outputting 1 in the case in
which all outputs of the voltage phase difference comparing unit
are 1 and outputting 0 in the rest of the case; and a second AND
gate outputting 1 in the case in which all outputs of the current
intensity comparing unit and the first AND gate are 1.
7. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 1, wherein the reverse load flow calculating
unit further comprises: a power receiving reverse load flow
calculating unit calculating power receiving direction reverse load
flow power; and a power transmitting reverse load flow calculating
unit calculating power transmitting direction reverse load flow
power.
8. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 1, wherein the reverse load flow calculating
unit further comprises: an active reverse load flow calculating
unit calculating active power of the reverse load flow power per
phase; and a reactive reverse load flow calculating unit
calculating reactive power of the reverse load flow power per
phase.
9. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 1, wherein the actual power usage calculating
unit further comprises: a power receiving actual power usage
calculating unit calculating power receiving direction
instantaneous compensation power per phase and 3 phase
instantaneous compensation power; and a power transmitting actual
power usage calculating unit calculating power transmitting
direction instantaneous compensation power per phase and 3 phase
instantaneous compensation power.
10. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 9, wherein the power receiving actual power
usage calculating unit or the power transmitting actual power usage
calculating unit further comprises: an instantaneous compensation
active power per phase calculating unit calculating instantaneous
compensation active power per phase; an instantaneous compensation
reactive power per phase calculating unit calculating instantaneous
compensation reactive power per phase; a 3 phase instantaneous
compensation active power calculating unit calculating
instantaneous compensation active power of 3 phase; and a 3 phase
instantaneous compensation reactive power calculating unit
calculating instantaneous compensation reactive power of 3
phase.
11. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 10, wherein the instantaneous compensation
active power per phase calculating unit calculates a compensation
value by subtracting reverse load flow instantaneous active power
per phase from instantaneous active power per phase.
12. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 10, wherein the instantaneous compensation
reactive power per phase calculating unit calculates a compensation
value by subtracting reverse load flow instantaneous reactive power
per phase from instantaneous reactive power per phase.
13. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 10, wherein the 3 phase instantaneous
compensation active power calculating unit calculates vector sum of
instantaneous active power per phase compensated at the same point
per phase.
14. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 10, wherein the 3 phase instantaneous
compensation reactive power calculating unit calculates vector sum
of instantaneous reactive power per phase compensated at the same
point per phase.
15. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 10, wherein the power transmitting/receiving
direction determining unit further comprises an active power
determining unit determining active power of the actual power usage
of the power transmitting direction or power receiving direction,
and a reactive power determining unit determining reactive power of
the actual power usage.
16. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 15, wherein the active power determining unit
outputs 0 if the sum of each compensated active power value per
phase and compensated 3 phase active power value is equal to or
smaller than 0, and does the sum of the each compensated active
power value per phase and the compensated 3 phase active power
value if it is higher than 0.
17. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 15, wherein the active power determining unit
outputs an output value if the sum of 3 phase active power values
is smaller than 0 and the sum of active power values per phase is
higher than 0.
18. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 15, wherein the active power determining unit
determines -active power if active power per phase is higher than a
measuring range in the case in which 3 phase active power is the
power receiving direction.
19. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 15, wherein the reactive power determining unit
determines a reactive power value if a compensation active power
value per phase is higher than 0 and active power of the power
receiving direction is determined, and outputs 0 for a reactive
power value if an active power value is smaller than 0 based on the
compensation active power value per phase.
20. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 19, wherein the reactive power determining unit
determines lagging reactive power or leading reactive power, in
which it selects the lagging reactive power if the compensated
reactive power per phase and 3 phase reactive power is higher than
0 and it does the leading reactive power if it is smaller than
0.
21. The bidirectional 3 phase power meter for compensating reverse
load flow of claim 1, wherein the power meter value storing unit
further comprises a power usage integrating unit integrating active
power or reactive power selected from the power
transmitting/receiving direction determining unit with time.
22. A method for metering by using a 3 phase bidirectional power
meter for compensating reverse load flow, comprising: (a) detecting
voltage or current per phase by using voltage value and current
value inputted from a sensor; (b) measuring neutral line current
and each phase difference per phase of power transmitting/receiving
direction by using the detected voltage value and current value;
(c) determining reverse load flow by using the measured each phase
difference per phase and the neutral line current; (d) calculating
reverse load flow power when it is determined for the occurrence of
the reverse load flow; (e) calculating instantaneous power by
employing an instantaneous power calculating function of the each
voltage per phase, the each current per phase and the phase
difference; (f) calculating actual power usage by calculating
instantaneous compensation power per phase and 3 phase
instantaneous compensation power through the instantaneous power
and the reverse load flow power; (g) determining active power of
the actual power usage; (h) determining reactive power of the
actual power usage; (i) measuring and storing amount of active
power or reactive power according to the result determined by the
active power or reactive power; and (j) calculating apparent power
or power factor using the measured active power or reactive power
amount.
23. The method of claim 22, wherein the step (b) comprises
determining power receiving direction by subtracting the phase of
the current per phase from the phase of the voltage per phase; and
determining power transmitting direction by adding 180.degree. to
the determined power receiving direction.
24. The method of claim 22, wherein the step (b) comprises
determining the neutral line current by calculating 3 phase current
vector sum and calculating 3 phase current by dividing
positive-sequence, negative-sequence, and zero-sequence.
25. The method of claim 22, wherein the step (c) comprises
outputting 1 if the zero-sequence is higher than the
negative-sequence when intensity of the negative-sequence is
compared with that of the zero-sequence and outputting 0 if it is
equal to or smaller.
26. The method of claim 22, wherein the step (a) further comprises
transforming into discrete signal by sampling the detected voltage
and the current per phase; and calculating non-sinusoidal wave
power by dividing the voltage per phase and current per phase
transformed into the discrete signal, into the intensity and phase
for each degree and DC component by employing the fast Fourier
transform.
27. The method of claim 26, wherein the step (g) further comprises
In the step of (g), per-phase instantaneous powers at a same point
are added, and if the three-phase-added value is greater than 0,
the power per phase and three-phase power can be accumulated in a
power-receiving direction. Furthermore, if the three-phase-added
value is less than 0, the power per phase and three-phase power can
be accumulated in a power-transmitting direction.
28. The method of claim 27, wherein the step (h) further comprises
adding reactive power per phase compensated at the same point per
phase.
29. The method of claim 27, wherein the step (h) further comprises
determining as lagging reactive power, if the compensated
instantaneous reactive power per phase and the compensated 3 phase
reactive power is higher than 0 and determining as leading reactive
power if it is smaller than 0.
30. The method of claim 22, wherein the step (i) further comprises
storing each of the compensated active power and reactive power
according to power receiving direction and power transmitting
direction.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 10-2010-0030568 filed on Apr. 2, 2010, with the
Korea Intellectual Property Office, the contents of which are
incorporated here by reference in their entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to a bidirectional 3 phase
power meter for compensating reverse load flow and a method for
metering thereby.
[0004] 2. Background
[0005] Problems metering excessively or insufficiently have been
caused due to a reverse load flow phenomenon in a power provider's
system, regardless of used power by a user or generated power.
[0006] Here, the reverse load flow refers to a energy that flows
from the load side to the source side, and is a ground source
supplied through the neutral line in a Yg-.DELTA. connection type.
Generally, no reverse load flow occurs in a .DELTA.-Y connection
type a receiving transformer, but the Yg-.DELTA. connection type is
a common connection of an interconnection transformer of DGs
(Distributed Power Generation).
[0007] Especially, such a reverse load flow phenomenon severely
occurs in a transmission and distribution power system
interconnected with distributed power occurrence such as
photovoltaic power occurrence, wind power occurrence and the like,
which causes an error therefore, regardless of accuracy of a power
meter.
[0008] A power meter calculates the price based on maximum power,
active power usage, and power factor. A calculation zone of a power
meter is the region where a reactive power region is overlapping to
an active power region.
[0009] In the reactive power region, there are various kinds of
var-hour (reactive power) meters as 0 to 180.degree. region is a
lagging reactive power zone, 60 to -120.degree. region is a lagging
and leading reactive power zone, and 90 to -90.degree. region is a
lagging and leading zone. For example, a reactive power meter of
the lagging zone of 0 to 180.degree. does not meter the leading
reactive power. However, the leading reactive power is metered
during the power transmission and this causes an error when power
factor is calculated. In the 60 to -120.degree. region, the leading
power and the lagging power are metered at the same time but the
region above 60.degree. cannot be metered. Therefore, it is the
most apparent that the active power region and the reactive power
region be overlapped as in the calculating zone.
[0010] In general, a power receiving consumer uses .DELTA.-Y wiring
method for an interconnection transformer and a power transmitting
consumer uses Yg-.DELTA. wiring method. A general load flow
direction of a power receiving consumer is the direction from a
power provider to a power user and a load flow direction of a power
transmitting consumer is the direction from a power user to a power
provider. When load flow per phase, unlike identical 3 phase load
flow, is mixed in a direction from a power supply side to a load
side or from a load side to a power supply side, a measurement
error may occure because load unbalance in a power system occurs
due to a wiring method of the interconnection transformer and a
load flow direction of one phase among 3 phases is thus changed
which is called as reverse load flow. This problem usually occurs
in the power transmitting side but it sometimes occurs in the power
receiving side due to a wiring system of the interconnection
transformer.
[0011] A conventional power transmitting side installs a power
receiving power meter and a power transmitting power meter and
calculates amount of power receiving power and amount of power
transmitting power, respectively. Here, in the power receiving
state, a power receiving power meter operates and in the power
transmitting state, a power transmitting power meter operates.
However, in the reverse load flow state, since a reverse load flow
is occurred in a power provider's system, a power receiving power
meter and a power transmitting power meter cause extremes
errors.
[0012] The power transmitting power meter has identical structure
to the power receiving power meter and a bidirectional power meter
measuring for both power transmitting and power receiving uses by
combining two of a one way metering system.
SUMMARY
[0013] The present invention is to provide a bidirectional 3 phase
power meter for compensating reverse load flow and a method for
metering thereby to increase reliability of power metering between
a power provider and a power user when a reverse load flow occurs
due to a system.
[0014] The present invention is to provide a bidirectional 3 phase
power meter for compensating reverse load flow and a method for
metering thereby to measure power transmitting/receiving usage,
except for reverse load flow when a reverse load flow occurs due to
a power system irrelevant to power equipments.
[0015] According to an aspect of the invention, there is provided a
bidirectional 3 phase power meter for compensating reverse load
flow including: a voltage/current detecting unit detecting a
voltage or current per phase; a bidirectional measuring unit
measuring power receiving direction or power transmitting direction
by calculating phase difference per phase using the detected
voltage per phase or current per phase and calculating neutral line
current; an instantaneous power calculating unit calculating
instantaneous power by using the voltage per phase, the current per
phase and the phase difference per phase; a reverse load flow
determining unit determining occurrence of reverse load flow
through the phase difference per phase and the neutral line current
calculated from the bidirectional measuring unit; a reverse load
flow calculating unit calculating reverse load flow power generated
when the reverse load flow determining unit determines occurrence
of reverse load flow; an actual power usage calculating unit
calculating actual power usage by calculating instantaneous
compensation power per phase and 3 phase instantaneous compensation
power using the instantaneous power and the reverse load flow
power; a power transmitting/receiving direction determining unit
determining active power or reactive power of the actual power
usage; a power meter value storing unit compensating the amount of
active power and reactive power calculated from the power
transmitting/receiving direction determining unit, and accumulating
and storing the result; and an apparent power/power factor
calculating unit calculating apparent power and power factor using
the active power and reactive power stored at the power meter value
storing unit and the amount of accumulated power.
[0016] The bidirectional measuring unit may further include a power
receiving direction measuring unit; and a power transmitting
direction measuring unit, in which the power receiving direction
measuring unit determines phase by subtracting the phase of the
current per phase from the phase of the voltage per phase, and the
power transmitting direction measuring unit determines phase by
adding 180.degree. to the phase determined at the power receiving
direction measuring unit.
[0017] The bidirectional measuring unit may further include a
neutral line current measuring unit measuring the neutral line
current by calculating 3 phase current vector sum.
[0018] The instantaneous power calculating unit may further include
a power receiving instantaneous power calculating unit calculating
power receiving direction instantaneous power; and a power
transmitting instantaneous power calculating unit calculating power
transmitting direction instantaneous power.
[0019] The power receiving instantaneous power calculating unit may
further include an instantaneous active power calculating unit
calculating instantaneous active power per phase; and an
instantaneous reactive power calculating unit calculating
instantaneous reactive power per phase.
[0020] The reverse load flow determining unit may further include:
a negative-sequence selecting unit selecting a negative-sequence
based on a smaller value from a positive-sequence and a
negative-sequence; a current intensity comparing unit outputting 0
or 1 by comparing a negative-sequence intensity outputted from the
negative-sequence selecting unit with a zero-sequence intensity; a
plurality of voltage phase difference comparing units outputting 0
or 1 by comparing phase difference of voltages per phase; a first
AND gate outputting 1 in the case in which all outputs of the
voltage phase difference comparing unit are 1 and outputting 0 in
the rest of the case; and a second AND gate outputting 1 in the
case in which all outputs of the current intensity comparing unit
and the first AND gate are 1.
[0021] The reverse load flow calculating unit may further include:
a power receiving reverse load flow calculating unit calculating
power receiving direction reverse load flow power; and a power
transmitting reverse load flow calculating unit calculating power
transmitting direction reverse load flow power.
[0022] The reverse load flow calculating unit may further include:
an active reverse load flow calculating unit calculating active
power of the reverse load flow power per phase; and a reactive
reverse load flow calculating unit calculating reactive power of
the reverse load flow power per phase.
[0023] The actual power usage calculating unit may further include:
a power receiving actual power usage calculating unit calculating
power receiving direction instantaneous compensation power per
phase and 3 phase instantaneous compensation power; and a power
transmitting actual power usage calculating unit calculating power
transmitting direction instantaneous compensation power per phase
and 3 phase instantaneous compensation power.
[0024] The power receiving actual power usage calculating unit or
the power transmitting actual power usage calculating unit may
further include: an instantaneous compensation active power per
phase calculating unit calculating instantaneous compensation
active power per phase; an instantaneous compensation reactive
power per phase calculating unit calculating instantaneous
compensation reactive power per phase; a 3 phase instantaneous
compensation active power calculating unit calculating 3 phase
instantaneous compensation active power; and a 3 phase
instantaneous compensation reactive power calculating unit
calculating 3 phase instantaneous compensation reactive power.
[0025] The instantaneous compensation active power per phase
calculating unit may calculate a compensation value by subtracting
reverse load flow instantaneous active power per phase from
instantaneous active power per phase.
[0026] The instantaneous compensation reactive power per phase
calculating unit may calculate a compensation value by subtracting
reverse load flow instantaneous reactive power per phase from
instantaneous reactive power per phase.
[0027] The 3 phase instantaneous compensation active power
calculating unit may calculate by a vector addition of
instantaneous active power per phase compensated at the same point
per phase.
[0028] The 3 phase instantaneous compensation reactive power
calculating unit may calculate by a vector addition of
instantaneous reactive power per phase compensated at the same
point per phase.
[0029] The power transmitting/receiving direction determining unit
may further include an active power determining unit determining
active power of the actual power usage of the power transmitting
direction or power receiving direction, and a reactive power
determining unit determining reactive power of the actual power
usage.
[0030] The active power determining unit may output 0 if the sum of
the compensated active power value per phase and compensated the 3
phase active power value is equal to or smaller than 0, and may
output the sum of the compensated active power value per phase and
the compensated 3 phase active power value if it is higher than
0.
[0031] The active power determining unit may output an output value
if the sum of 3 phase active power values is smaller than 0 and the
sum of active power values per phase is higher than 0.
[0032] The active power determining unit may determine -active
power if active power per phase is higher than a measuring range in
the case in which 3 phase active power is the power receiving
direction.
[0033] The reactive power determining unit may determine a reactive
power value if a compensation active power value per phase is
higher than 0 and active power of the power receiving direction is
then determined, and output 0 for a reactive power value if an
active power value is smaller than 0 based on the compensation
active power value per phase.
[0034] The reactive power determining unit may determine lagging
reactive power or leading reactive power, in which it may select
the lagging reactive power if the compensated reactive power per
phase and 3 phase reactive power is higher than 0 and it does the
leading reactive power if it is smaller than 0.
[0035] The power meter value storing unit may further include a
power usage integrating unit integrating active power or reactive
power selected from the power transmitting/receiving direction
determining unit with time.
[0036] According to another aspect of the invention, there is
provided a method for metering by a 3 phase bidirectional power
meter for compensating reverse load flow, including: (a) detecting
voltage or current per phase by using voltage value and current
value inputted from a sensor; (b) measuring neutral line current
and each phase difference per phase of the power
transmitting/receiving direction by using the detected voltage
value and current value per phase; (c) determining reverse load
flow by using the measured each phase difference per phase and the
neutral line current; (d) calculating reverse load flow power when
it is determined for the occurrence of the reverse load flow; (e)
calculating instantaneous power by employing an instantaneous power
calculating function of the each voltage per phase, the each
current per phase and the phase difference; (f) calculating actual
power usage by calculating instantaneous compensation power per
phase and 3 phase instantaneous compensation power through the
instantaneous power and the reverse load flow power; (g)
determining active power of the actual power usage; (h) determining
reactive power of the actual power usage; (i) measuring and storing
amount of active power or reactive power according to the
determined active power or reactive power; and (j) calculating
apparent power or power factor using the measured active power or
reactive power amount.
[0037] The step (b) may include determining power receiving
direction by subtracting the phase of the current per phase from
the phase of the voltage per phase; and determining power
transmitting direction by adding 180.degree. to the determined
power receiving direction.
[0038] The step (b) may include determining the neutral line
current by calculating 3 phase current vector sum and calculating 3
phase current with positive-sequence, negative-sequence, and
zero-sequence.
[0039] The step (c) may include outputting 1 if the zero-sequence
is higher than the negative-sequence when intensity of the
negative-sequence is compared with that of the zero-sequence and
outputting 0 if it is equal to or smaller.
[0040] The step (a) may further include transforming the detected
voltage per phase and the detected current per phase into discrete
signal by sampling; and calculating non-sinusoidal wave power by
dividing the voltage per phase and the current per phase which are
transformed into the discrete signal, into the intensity and phase
for each degree and DC component by employing the fast Fourier
transform.
[0041] In the step of (g), per-phase instantaneous powers at a same
point are added, and if the three-phase-added value is greater than
0, the power per phase and three-phase power can be accumulated in
a power-receiving direction. Furthermore, if the three-phase-added
value is less than 0, the power per phase and three-phase power can
be accumulated in a power-transmitting direction.
[0042] The step (h) may further include adding reactive power per
phase compensated at the same point per phase.
[0043] The step (h) may further include determining as lagging
reactive power if the compensated instantaneous reactive power per
phase and the compensated 3 phase reactive power is higher than 0
and determining as leading reactive power if it is smaller than
0.
[0044] The step (i) may further include storing each of the
compensated active power and reactive power according to power
receiving direction and power transmitting direction.
[0045] According to the exemplary embodiment of the present
invention, it allows measuring accurate power usage actually used
by a user by compensating errors caused by reverse load flow in a
power system and controlling peaks and power factor by using
compensated active/reactive power per phase.
[0046] In addition, according to the exemplary embodiment of the
present invention, it allows checking metered values per phase in
case of absent phase or absent line errors of PT or CT per
phase.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a schematic block view illustrating a
bidirectional 3 phase power meter for compensating reverse load
flow according to an embodiment of the present invention.
[0048] FIG. 2 and FIG. 3 are schematic block views illustrating a
voltage/current detecting unit in FIG. 1.
[0049] FIG. 4 to FIG. 7 are schematic drawings illustrating a
bidirectional measuring unit in FIG. 1.
[0050] FIG. 8 is a block view illustrating a power receiving
instantaneous power calculating unit according to an embodiment of
the present invention.
[0051] FIG. 9 is a block view illustrating a power transmitting
instantaneous power according to an embodiment of the present
invention.
[0052] FIG. 10 to FIG. 12 are block views illustrating an example
of a reverse load flow determining unit in FIG. 1.
[0053] FIG. 13 to FIG. 16 are block views illustrating an example
of a power receiving reverse load flow determining unit in FIG.
1.
[0054] FIG. 17 to FIG. 21 are block views illustrating an example
of a power receiving actual power usage calculating unit in FIG.
1.
[0055] FIG. 22 to FIG. 25 are block views illustrating an example
of a power receiving direction determining unit in FIG. 1.
[0056] FIG. 26 is a block view illustrating an example of a power
receiving active power storing unit in FIG. 1.
[0057] FIG. 27 a block view illustrating an example of a power
receiving lagging reactive power storing unit in FIG. 1.
[0058] FIG. 28 a block view illustrating an example of a power
receiving leading reactive power storing unit in FIG. 1.
[0059] FIG. 29 to FIG. 31 are block views illustrating an example
of a power receiving direction apparent power/power factor
calculating unit.
[0060] FIG. 32 to FIG. 35 are block views illustrating an example
of a power transmitting reverse load flow calculating unit in FIG.
1.
[0061] FIG. 36 to FIG. 40 are block views illustrating an example
of a power transmitting actual power usage calculating unit in FIG.
1.
[0062] FIG. 41 to FIG. 44 are block views illustrating an example
of a power transmitting direction determining unit in FIG. 1.
[0063] FIG. 45 is a block view illustrating an example of a power
transmitting active power storing unit in FIG. 1.
[0064] FIG. 46 is a block view illustrating an example of a power
transmitting lagging reactive power storing unit in FIG. 1.
[0065] FIG. 47 is a block view illustrating an embodiment of a
power transmitting leading reactive power storing unit in FIG.
1.
[0066] FIG. 48 to FIG. 50 are block view illustrating an embodiment
of a power transmitting direction apparent power/power factor
calculating unit.
[0067] FIG. 51 is a flow chart illustrating a method for metering
by a 3 phase bidirectional system for compensating reverse load
flow according to an embodiment of the present invention.
DETAILED DESCRIPTION
[0068] While the present invention has been described with
reference to particular embodiments, it is to be appreciated that
various changes and modifications may be made by those skilled in
the art without departing from the spirit and scope of the present
invention, as defined by the appended claims and their
equivalents.
[0069] Throughout the description of the present invention, when
describing a certain technology is determined to evade the point of
the present invention, the pertinent detailed description will be
omitted. While such terms as "first" and "second," etc., may be
used to describe various components, such components must not be
limited to the above terms. The above terms are used only to
distinguish one component from another.
[0070] The bidirectional 3 phase power meter for compensating
reverse load flow and the method for metering thereby according to
certain embodiments of the invention will be described below in
more detail with reference to the accompanying drawings.
[0071] FIG. 1 is a schematic block view illustrating a
bidirectional 3 phase power meter for compensating reverse load
flow according to an embodiment of the present invention.
[0072] According to FIG. 1, a bidirectional 3 phase power meter for
compensating reverse load flow may include a voltage/current
detecting unit 60, a bidirectional measuring unit 61, a power
receiving instantaneous power calculating unit 62, a power
transmitting instantaneous power calculating unit 63, a reverse
load flow determining unit 64, a power receiving reverse load flow
calculating unit 65, a power transmitting reverse load flow
calculating unit 66, a power receiving actual power usage
calculating unit 67, a power receiving direction determining unit
69, an active power storing unit 75, a lagging reactive power
storing unit 76, a leading reactive power storing unit 77, a power
receiving direction apparent power/power factor calculating unit
81, a power transmitting actual power usage calculating unit 68, a
power transmitting direction determining unit 70, an active power
storing unit 78, a lagging reactive power storing unit 79, a
leading reactive power storing unit 80 and a power transmitting
direction apparent power/power factor calculating unit 82.
[0073] Particularly, the voltage/current detecting unit 60 may
detect voltage/current per phase by using a detecting sensor such
as potential transformer 601 (PT) and current transformer 602 (CT)
and the like. As shown in FIG. 2, the potential transformer 601 may
be arranged between a power supply side and a load side and between
a neutral line and each power line per phase to detect each voltage
per phase.
[0074] In the potential transformer 601, + side of voltage per
phase Va, Vb, Vc may be connected to a voltage line per phase and -
side is connected to a neutral line based on polarity of the
voltage and current per phase.
[0075] The current transformer 602 may be arranged in parallel
between the power supply side and the load side to detect each
current per phase. In the current transformer 602, a determination
reference of current per phase Ia, Ib, Ic is that + side is a power
supply side and - side is a load side.
[0076] Signals of the detected voltage and current per phase, which
are continuous signals, are converted to discrete signals at a
sampler 603 and further divided into intensity per degree 604,
phase per degree 607, DC component 605 at a fast Fourier transform
unit 606 to calculate non-sinusoidal wave power. The non-sinusoidal
wave power may be determined by dividing into a fundamental
component, a harmonic component, a DC component through the fast
Fourier transform (FFT). The present invention will describe for
the fundamental component, not for the harmonic component and the
DC component since only a fundamental component is generated due to
a reverse load flow phenomenon caused by an interconnection
transformer in embodiments of the present invention.
[0077] The bidirectional measuring unit 61 may measure neutral line
current and phase angle of the power transmitting/receiving
direction by using the voltage and current determined at the
voltage and current detecting unit 60. As shown in FIG. 4 to FIG.
7, the bidirectional measuring unit 61 may include a phase per
phase measuring unit 611 and a neutral line current measuring unit
612.
[0078] The phase per phase measuring unit 611 may measure phase
angle per phase .theta.a, .theta.b, .theta.c by subtracting phase
of current per phase Ia_p, Ib_p, Ic_p from phase of voltage per
phase Va_p, Vb_p, Vc_p as shown in FIG. 6 to determine phase angle
of the power receiving direction. Further, the phase per phase
measuring unit 611 may measure the power transmitting direction
based on phase angle .theta.a2, .theta.b2, .theta.c2 by adding
180.degree. to the phase difference of the power receiving
direction as shown in FIG. 7.
[0079] The neutral line current measuring unit may measure current
of the neutral line which is vector sum of current per phase Ia,
Ib, Ic calculated at a 3 phase current vector sum calculating unit
614. Here, the current of the neutral line may be determined by one
method chosen from the following methods: (i) dividing 3 phase
current into a positive-sequence, a negative-sequence and a
zero-sequence using the method of symmetrical coordinates 615; (ii)
indirectly determining 3 phase current inside the power meter; and
(iii) directly determining current of primary neutral line of an
interconnection transformer.
[0080] A power receiving instantaneous power calculating unit 62
may calculate instantaneous power of the power receiving direction.
Here, the power receiving instantaneous power calculating unit 62
may include a power receiving instantaneous active power per phase
calculating unit 621 and a power receiving instantaneous reactive
power per phase calculating unit 622 as shown in FIG. 8.
[0081] The power receiving instantaneous active power per phase
calculating unit 621 may calculate by employing functions for
calculating active power of Equation 1 to Equation 3:
Pa1=Va.sub.--m*Ia.sub.--m*cos .theta.a Equation 1
[0082] (Pa1 is active power of a phase, Va_m is voltage of a phase,
Ia_m is current of a phase, .theta.a is phase angle);
Pb1=Vb.sub.--m*Ib.sub.--m*cos .theta.b Equation 2
[0083] (Pb1 is active power of b phase, Vb_m is voltage of b phase,
Ib_m is current of b phase, .theta.b is phase angle); and
Pc1=Vc.sub.--m*Ic.sub.--m*cos .theta.c Equation 3
[0084] (Pc1 is active power of c phase, Vb_m is voltage of c phase,
Ic_m is current of c phase, .theta.c is phase angle).
[0085] The power receiving instantaneous reactive power per phase
calculating unit 622 may calculate by employing functions for
calculating reactive power of Equation 4 to Equation 6:
Qa1=Va.sub.--m*Ia.sub.--m*sin .theta.a Equation 4
[0086] (Qa1 is reactive power of a phase, Va_m is voltage of a
phase, Ia_m is current of a phase, .theta.a is phase angle);
Qb1=Vb.sub.--m*Ib.sub.--m*sin .theta.b Equation 5
[0087] (Qb1 is reactive power of b phase, Vb_m is voltage of b
phase, Ib_m is current of b phase, .theta.b is phase angle);
and
Qc1=Vc.sub.--m*Ic.sub.--m*sin .theta.c Equation 6
[0088] (Qc1 is reactive power of c phase, Vb_m is voltage of c
phase, Ic_m is current of c phase, .theta.c is phase angle).
[0089] The power receiving instantaneous power calculating unit 62
can calculate instantaneous active power and reactive power per
phase of the power receiving direction as in Equations 1 to 6.
[0090] The power transmitting instantaneous power calculating unit
63 can calculate instantaneous power of the power transmitting
direction. Here, the power transmitting instantaneous power
calculating unit 63 may include a power transmitting instantaneous
active power per phase calculating unit 631 and a power
transmitting instantaneous reactive power per phase calculating
unit 632 as shown in FIG. 9.
[0091] The power transmitting instantaneous active power per phase
calculating unit 631 may calculate by employing functions for
calculating active power of Equation 7 to Equation 9:
Pa2=Va.sub.--m*Ia.sub.--m*cos .theta.a2 Equation 7
[0092] (Pa2 is active power of a phase, Va_m is voltage of a phase,
Ia_m is current of a phase, .theta.a2 is phase angle);
Pb2=Vb.sub.--m*Ib.sub.--m*cos .theta.b2 Equation 8
[0093] (Pb2 is active power of b phase, Vb_m is voltage of b phase,
Ib_m is current of b phase, .theta.b2 is phase angle); and
Pc2=Vc.sub.--m*Ic.sub.--m*cos .theta.c2 Equation 9
[0094] (Pc2 is active power of c phase, Vb_m is voltage of c phase,
Ic_m is current of c phase, .theta.c is phase angle).
[0095] The instantaneous reactive power per phase calculating unit
of the power transmitting direction 632 may calculate by employing
functions for calculating reactive power of Equation 10 to Equation
12:
Qa2=Va.sub.--m*Ia.sub.--m*sin .theta.a2 Equation 10
[0096] (Qa2 is reactive power of a phase, Va_m is voltage of a
phase, Ia_m is current of a phase, .theta.a2 is phase angle);
Qb2=Vb.sub.--m*Ib.sub.--m*sin .theta.b2 Equation 11
[0097] (Qb1 is reactive power of b phase, Vb_m is voltage of b
phase, Ib_m is current of b phase, .theta.b2 is phase angle);
and
Qc2=Vc.sub.--m*Ic.sub.--m*sin .theta.c2 Equation 12
[0098] (Qc2 is reactive power of c phase, Vb_m is voltage of c
phase, Ic_m is current of c phase, .theta.c2 is phase angle).
[0099] The power transmitting instantaneous power calculating unit
63 can calculate instantaneous active power and reactive power per
phase of the power transmitting direction as in Equations 7 to
12.
[0100] The reverse load flow determining unit 64 may determine
whether to compensate for reverse load flow by comparing the
intensity of a load current when the reverse load flow is caused in
a power system. Further, the reverse load flow determining unit 64
may determine each reverse load flow of the power receiving
direction and the power transmitting direction.
[0101] The reverse load flow determining unit 64 may include a
current intensity comparing unit 641, a negative-sequence selecting
unit 642, a voltage phase difference comparing unit 643, a first
AND gate 644, and a second AND gate 645 as shown FIGS. 10 to
12.
[0102] The current intensity comparing unit 641 may compare the
intensity of a negative-sequence is 2 and that of a zero-sequence
is 0 when the reverse load flow is caused in a power system. Here,
when the intensity of the negative-sequence is higher than that of
the zero-sequence, the current intensity comparing unit 641 may
determine as reverse load flow and output 1 at 1_rev, while it may
output 0 for the rest of cases.
[0103] The negative-sequence selecting unit 642 may select
negative-sequence based on a smaller value from a positive-sequence
and a negative-sequence since when a rotation direction of 3 phase
current changes, a positive-sequence and a negative-sequence are
changed.
[0104] In addition, because a reverse load flow occurs in a 3 phase
system, a method for determining 3 phase power supply is to output
1 at V_rev when phase difference of voltage per phase (Va_p and
Vb_p, Vb_p and Vc_p, Vc_p and Va_p) exceeds 90.degree. by using the
voltage phase difference comparing unit 643 and the first AND gate
644 and output 0 for the rest of cases.
[0105] The second AND gate 645 outputs 0 or 1 by employing output
of the current intensity comparing unit 641 and output of the first
AND gate 644.
[0106] A reverse load flow phenomenon in a power supply system is
caused by load variations in the system and when power caused by
the reverse load flow is higher than actual power transmitted and
received by the user, a measurement error occurs, while when power
caused by the reverse load flow is smaller than actual power
transmitted and received by the user, a measurement error does not
occur.
[0107] The power receiving reverse load flow calculating unit 65
may calculate amount of power receiving reverse load flow power if
the reverse load flow determining unit 64 determines as power
receiving direction reverse load flow.
[0108] According to FIG. 13 to FIG. 16, the power receiving reverse
load flow calculating unit 65 may include a power receiving reverse
load flow phase angle per phase calculating unit 657, a power
receiving active reverse load flow per phase calculating unit 651
and a power receiving reactive reverse load flow per phase
calculating unit 654.
[0109] The power receiving reverse load flow phase angle per phase
calculating unit 657 calculates phase difference .THETA.na,
.THETA.nb, .THETA.nc by adding 180.degree. to each phase of voltage
per phase and substrating phase In_p of neutral line current.
[0110] The calculated phase difference value is provided to the
power receiving active reverse load flow per phase calculating unit
651 and the power receiving reactive reverse load flow per phase
calculating unit 654.
[0111] The power receiving active reverse load flow per phase
calculating unit 651 may calculate with functions of active power
of reverse load flow per phase as shown in Equations 13 to 15:
Pna1=Va.sub.--m*In.sub.--m*cos .theta.na/3 Equation 13
[0112] (wherein, Pna1 is active power of a phase during the reverse
load flow, Va_m is voltage of a phase, In_m is neutral line
current, .theta.na is phase difference during the reverse load
flow);
Pnb1=Vb.sub.--m*In.sub.--m*cos .theta.nb/3 Equation 14
[0113] (wherein, Pnb1 is active power of b phase during the reverse
load flow, Vb_m is voltage of b phase, In_m is neutral line
current, .theta.nb is active power of b phase during the reverse
load flow); and
Pnc1=V.sub.--cm*In.sub.--m*cos .theta.nc/3 Equation 15
[0114] (wherein, Pnc1 is active power of c phase during the reverse
load flow, Vc_m is voltage of c phase, In_m is neutral line
current, .theta.nc is phase difference of c phase during the
reverse load flow).
[0115] The power receiving active reverse load flow per phase
calculating unit 651 can calculate each of active powers Pna1,
Pnb1, Pnc1 generated by reverse load flow in the power receiving
direction. The power receiving active reverse load flow per phase
calculating unit 651 can calculate the active power Pna1, Pnb1,
Pnc1 by use of a current value, which is obtained by dividing the
neutral line current into 3, and a phase difference, which the
phase of a phase current subtracted by the phase of the neutral
line current, since the intensity (In_m) of the neutral line
current is three times greater than that of the phase current when
the reverse load flow occurs.
[0116] The power receiving reactive reverse load flow per phase
calculating unit 654 may calculate with functions of reactive power
of reverse load flow per phase as shown in Equations 16 to 18:
Qna1=Va.sub.--m*In.sub.--m*sin .theta.na/3 Equation 16
[0117] (wherein, Qna1 is reactive power of a phase during the
reverse load flow, Va_m is voltage of a phase, In_m is neutral line
current, .theta.na is phase difference of a phase during the
reverse load flow);
Qnb1=Vb.sub.--m*In.sub.--m*sin .theta.nb/3 Equation 17
[0118] (wherein, Qnb1 is reactive power of b phase during the
reverse load flow, Vb_m is voltage of b phase, In_m is neutral line
current, .theta.nb is phase difference of b phase during the
reverse load flow); and
Qnc1=Vc.sub.--m*In.sub.--m*sin .theta.nc/3 Equation 18
[0119] (wherein, Pnc1 is reactive power of c phase during the
reverse load flow, Vc_m is voltage of c phase, In_m is neutral line
current, .theta.nc is phase difference of c phase during the
reverse load flow)
[0120] The power receiving reactive reverse load flow per phase
calculating unit 654 can calculate each of reactive powers Qna1,
Qnb1, Qnc1 generated by reverse load flow in the power receiving
direction. The power receiving active reverse load flow per phase
calculating unit 654 can calculate the reactive power Qna1, Qnb1,
Qnc1 by use of a current value, which is obtained by dividing the
neutral line current into 3, and a phase difference, which the
phase of a phase current subtracted by the phase of the neutral
line current, since the intensity (In_m) of the neutral line
current is three times greater than that of the phase current when
the reverse load flow occurs.
[0121] The reverse load flow determining unit 64 may determine
whether a reverse load flow occurs or not by comparing the
intensity of load current per phase when a reverse load flow occurs
with that of the neutral line current in a system. Because multiple
functions 653, 656 multiple 1 to a rev value when a reverse load
flow occurs, while they do 0 when a reverse load flow does not
occur to determine whether to compensate active, reactive power
caused by the reverse load flow, the reverse load flow determining
unit 64 is thus able to determine whether to compensate active
power and reactive power according to the occurence of the reverse
load flow.
[0122] The power receiving actual power usage calculating unit 67
may calculate actual power usage by employing the instantaneous
power value inputted from the power receiving instantaneous power
calculating unit 62 and the reverse load flow power value inputted
from the power receiving reverse load flow calculating unit 65.
[0123] For this purpose, the power receiving actual power usage
calculating unit 67 may include a power receiving instantaneous
compensation active power per phase calculating unit 671, a power
receiving instantaneous compensation reactive power per phase
calculating unit 672, a 3 phase power receiving instantaneous
compensation active power per phase calculating unit 673 and a 3
phase power receiving instantaneous compensation reactive power per
phase calculating unit 674 As shown FIG. 17 to FIG. 21, the power
receiving instantaneous compensation active power per phase
calculating unit 671 may calculate each out value Pa10, Pb10, Pc10
of compensated instantaneous active power per phase traded between
a provider and a user by subtracting reverse load flow
instantaneous active power per phase, Pna1, Pnb1, Pnc1 from the
power receiving instantaneous active power per phase, Pa1, Pb1,
Pc1.
[0124] The power receiving instantaneous compensation reactive
power per phase calculating unit 672 may calculate each out value
Qa10, Qb10, Qc10 of compensated instantaneous reactive power per
phase traded between a provider and a user by subtracting the
reverse load flow instantaneous reactive power per phase, Qna1,
Qnb1, Qnc1 from the power receiving instantaneous reactive power
per phase Qa1, Qb1, Qc1.
[0125] The 3 phase power receiving instantaneous compensation
active power calculating unit 673 may calculate 3 phase power
receiving instantaneous compensation active power P34_10 by
conducting vector sum with a 3 terminal addition function for
instantaneous power per phase Pa10, Pb10, Pc10 compensated at the
same point per phase to determine 3 phase active power. Further,
the 3 phase power receiving instantaneous compensation reactive
power calculating unit 674 may calculate 3 phase power receiving
instantaneous compensation reactive power Q34_10 by conducting
vector sum with a 3 terminal addition function for reactive power
per phase Qa10, Qb10, Qc10 compensated at the same point per phase
to determine 3 phase reactive power.
[0126] The power receiving direction determining unit 69 may
determine power transmitting direction un-metered usage, active
power and reactive power from the calculated actual power usage
value to store actual power usage value.
[0127] As shown in FIG. 22, the power receiving direction
determining unit 69 may include a power receiving active power
determining unit 71 and a power receiving reactive power
determining unit 73.
[0128] As shown in FIG. 23, the power receiving active power
determining unit 71 may output 0 if the active power value Pa10,
Pb10, Pc10, P34_10 compensated at the intensity selecting unit 712
is equal to or smaller than 0, and output active power value Pa10s,
Pb10s, Pc10s, P34_10s if it is higher than 0.
[0129] As shown in FIG. 24, the power receiving active power
determining unit 71 may input at a AND gate 744 after comparing the
intensity of compensated active power Pa10 of a phase at an
intensity selecting unit 713 and input at a AND gate 744 after
comparing the intensity of compensated 3 phase active power P34_10
at an intensity selecting unit 713. The AND gate 744 outputs DFA if
both inputted values are 1.
[0130] For example, the intensity selecting unit 713 outputs 0 if
the intensity of compensated active power Pa10 of a phase is equal
to or smaller than 0 and outputs 1 if it is higher than 0 and then
inputs the result to the AND gate 744. Here, if both the intensity
of compensated active power Pa10 of a phase and the intensity of
compensated 3 phase active power P34_10 are higher than 0, it is
able to output DFA.
[0131] DFB and DFC may be outputted by calculating for the other b
and c phase as described above. 0 is outputted if the compensated 3
phase active power P34_10 is equal to or smaller than 0 and 1 is
outputted if it is higher than 0.
[0132] That is, reverse direction per phase of the power receiving
direction is detected when the sum of 3 phase active power of the
power receiving direction is smaller than 0 and the active power
per phase of the power receiving direction is higher than 0 to
output out value DFA, DFB, DFC.
[0133] As shown in FIG. 25, the power receiving reactive power
determining unit 73 may determine reactive power value Qa10, Qb10,
Qc10, Q34_10 if the intensity selecting unit 713 determines active
power of the power receiving direction when the compensated active
power per phase Pa10s, Pb10s, Pc10s, P34_10s is higher than 0, and
output 0 for a reactive power value at the multiple function 653 if
active power Pa10s, Pb10s, Pc10s, P34_10s is smaller than 0.
[0134] The power receiving reactive power determining unit 73 may
divide the outputted reactive power to lagging reactive power and
leading reactive power. As shown in FIG. 25, the intensity
selecting unit 712 outputs lagging reactive power Qa11, Qb11, Qc11,
3Q11 if the compensated reactive power per phase and the
compensated reactive power of 3 phase of the power receiving
direction Qa10, Qb10, Qc10, Q34_10 are higher than 0, and outputs
leading reactive power Qa12, Qb12, Qc12, 3Q12 if they are smaller
than 0.
[0135] A conventional power meter determines a metered value per
phase with power transmitting, receiving direction or 0 if active
power per phase deviates from 0-.+-.90.degree.. However, power
receiving direction and power transmitting direction is determined
based on the sum of 3 phase powers in order to prevent such a
problem in the present invention. In addition, if 3 phase active
power is the power receiving direction and active power per phase
exceeds a metering range, `-` active power is measured and lagging
reactive power which exceeds a metering range is calculated with
leading reactive power. In contrast, leading reactive power is
calculated with lagging reactive power.
[0136] The power transmitting direction and the power receiving
direction are determined by the intensity of 3 phase active power,
and lagging reactive power and leading reactive power are
determined by the intensity of 3 phase lagging reactive power and 3
phase leading reactive power based on the determined 3 phase active
power.
[0137] The sum of 3 phase active power of the power receiving
direction is equal to the sum of active power per phase of the
power receiving direction, the sum of 3 phase lagging reactive
power of the power receiving direction is equal to the sum of
lagging reactive power per phase of the power receiving direction,
and the sum of 3 phase leading reactive power of the power
receiving direction is equal to the sum of leading reactive power
per phase of the power receiving direction.
[0138] For example, if a phase among a, b, c phases is reverse
direction load flow exceeding a metering range, b and c phase are
normally determined and the power receiving direction P34F and the
power transmitting direction P34R are first determined based on the
intensity of 3 phase active power and active power per phase is
calculated by the direction P34F of 3 phase active power.
[0139] The power receiving direction active power storing unit 75
may include a power receiving direction active power per phase
metering unit 751, a power receiving direction 3 phase active power
integrating unit 752, a power receiving direction active power
storing unit, and a power receiving direction 3 phase active power
storing unit as shown in FIG. 1 and FIG. 26.
[0140] The power receiving direction active power per phase
metering unit 751 determines 0 for a phase active power Pa10s of
the power receiving direction when reverse direction load flow
occurs in a phase and determines a phase active power of the power
transmitting direction Pa20s as shown in FIG. 26. Here, if 3 phase
active power of the power transmitting direction P34_20 is smaller
than 0 and a phase active power of the power transmitting direction
Pa20 is higher than 0, DRA outputs 1 and a phase active power is
determined as "-" by a 2 terminal subtraction unit 671, and out
value of DRB and DRC of b and c phase is 0 and reverse direction
power is not determined. The power receiving direction active power
usage integrating unit 752 integrates active power value calculated
per phase and 3 phase active power usage accumulated value 753 by
time.
[0141] The power receiving active power per phase storing unit and
the 3 phase power receiving active power storing unit may store
amount of active power per phase and amount of 3 phase active
power, respectively.
[0142] As shown in FIG. 27, the power receiving direction lagging
reactive power storing unit 76 may include a power receiving
lagging reactive power per phase metering unit 761, a 3 phase power
receiving lagging reactive power integrating unit 762, a power
receiving lagging reactive power per phase storing unit, and a 3
phase power receiving lagging reactive power storing unit.
[0143] The power receiving lagging reactive power per phase
metering unit 761 determines 0 for a phase lagging reactive power
Qa11 of the power receiving direction based on a phase and a phase
leading reactive power Qa22 of the power transmitting direction
when reverse direction load flow occurs in a phase. Here, 1 is
outputted as a condition value (DRA) to determine a phase reactive
power toward the power receiving direction and lagging reactive
power of the power receiving direction Qa11 and leading reactive
power of the power transmitting direction Qa22 are determined with
a phase lagging reactive power by employing 2 terminal addition
function, and out value of DRB and DRC of b and c phase is 0 and
leading reactive power is not determined. Here, the 3 phase lagging
reactive power of the power receiving direction is equal to the sum
of lagging reactive power per phase.
[0144] The lagging reactive power usage integrating unit of the
power receiving direction 762 integrates the lagging reactive power
value calculated per phase and 3 phase lagging reactive power usage
accumulated value by time.
[0145] The leading reactive power storing unit of the power
receiving direction 77 may include a power receiving leading
reactive power per phase metering unit 771, a 3 phase power
receiving lagging reactive power integrating unit 772, a power
receiving lagging reactive power per phase storing unit and a 3
phase power receiving lagging reactive power storing unit.
[0146] The power receiving leading reactive power per phase
metering unit 771 determines the leading reactive power as 0 when
reverse direction load flow occurs in a phase because a phase
leading reactive power of the power receiving direction Qa12 does
not determine a phase active power based on a phase. Here, 1 is
outputted as a condition value (DRA) to determine a phase reactive
power toward the power receiving direction and a phase lagging
reactive power of the power receiving direction Qa21 is determined
as 0. The a phase leading reactive power of the power receiving
direction Qa12 and the a phase lagging reactive power of the power
receiving direction Qa21 are outputted as a phase leading reactive
power by employing 2 terminal addition function, and out value of
DRB and DRC of b and c phase is 0 and lagging reactive power is not
determined. Here, the 3 phase leading reactive power of the power
receiving direction is equal to the sum of leading reactive power
per phase.
[0147] The leading reactive power usage integrating unit of the
power receiving direction 772 integrates leading reactive power
value calculated per phase and 3 phase leading reactive power value
by time.
[0148] The compensated power receiving active power Pa10_rms,
Pb10_rms, Pc10_rms, 3P10_rms, the lagging reactive power Qa11_rms,
Qb11_rms, Qc11_rms, 3Q11_rms, the leading reactive power Qa12_rms,
Qb12_rms, Qc12_rms, 3Q12_rms are stored and outputted and the
amount of active power Pa10_kwh, Pb10_kwh, Pc10_kwh, 3P10_kwh, the
lagging reactive power usage Qa11_kvarh, Qb11_kvarh, Qc11_kvarh,
3Q11_kvarh, the leading reactive power usage Qa12_kvarh,
Qb12_kvarh, Qc12_kvarh, 3Q12_kvarh are accumulated and stored
according to a metering function by time.
[0149] A power receiving apparent power/power factor calculating
unit 81 calculates apparent power and power factor and outputs the
calculated values. As shown in FIG. 29, the power receiving
apparent power/power factor calculating unit 81 may include an
apparent power calculating unit 811 and a power factor calculating
unit 812.
[0150] For example, as shown in FIG. 30, the power receiving
apparent power calculating unit 811 may calculate apparent power
per phase and 3 phase power receiving apparent power. Here, the
power receiving apparent power calculating unit 811 may calculate
each apparent power per phase and amount of apparent power 1Sa,
1Sb, 1Sc, 3S1 by employing functions for calculating apparent power
of Equation 19 to Equation 22 by using power receiving RSM
value-treated active power, lagging reactive power, leading
reactive power and accumulated usage.
1Sa= {square root over
(Pa10.sub.kwh.sup.2+(Qa11.sub.kvarh+Qa12.sub.kvarh).sup.2)}
Equation 19
[0151] (wherein, Pa10 is active power of a phase, Qa11 is lagging
active power of a phase, Qa12 is leading reactive power of a
phase)
1Sb= {square root over
(Pb10.sub.kwh.sup.2+(Qb11.sub.kvarh+Qb12.sub.kvarh).sup.2)}
Equation 20
[0152] (wherein, Pa10 is active power of b phase, Qa11 is lagging
reactive power of b phase, Qa12 is leading reactive power of b
phase)
1Sc= {square root over
(Pc10.sub.kwh.sup.2+(Qc11.sub.kvarh+Qc12.sub.kvarh).sup.2)}
Equation 21
[0153] (wherein, Pc10 is active power of c phase, Qc11 is lagging
reactive power of c phase, Qc12 is leading reactive power of c
phase)
3S1= {square root over
(3P10.sub.kwh.sup.2+(3Q11.sub.kvarh+3Q12.sub.kvarh).sup.2)}
Equation 22
[0154] As shown in FIG. 31, the power receiving power factor
calculating unit 812 may calculate power receiving power factor per
phase and 3 phase power receiving power factor by employing power
factor calculating functions with using power receiving active
power and usage Pa10_kwh, Pb10_kwh, Pc10_kwh, 3P10_kwh and apparent
power and apparent power usage 1Sa, 1Sb, 1Sc, 3S1.
[0155] Equation 23 to Equation 26 are equations for power receiving
power factors and 3 phase power receiving power factors of a, b,
and c phase.
A cos .theta.10=Pa10_kwh/1Sa Equation 23
B cos .theta.10=Pb10_kwh/1Sb Equation 24
C cos .theta.10=Pc10_kwh/1Sc Equation 25
3 cos .theta.10=3P10_kwh/3S1 Equation 26
[0156] A power transmitting reverse load flow calculating unit 66
in FIG. 1 and FIG. 32 may include a reverse load flow phase angle
per phase calculating unit 667, a active reverse load flow per
phase calculating unit 661 and a reactive reverse load flow per
phase calculating unit 662 which have identical functions described
in the power receiving reverse load flow calculating unit 65.
[0157] As shown in FIG. 33, the reverse load flow phase angle per
phase calculating unit 667 may calculate phase angle per phase
.theta.na2, .theta.nb2, .theta.nc2 by subtracting phase of neutral
line current (In_p) from phase of input voltage per phase Va_p,
Vb_p, Vc_p.
[0158] As shown in FIG. 34, the active reverse load flow per phase
calculating unit 661 may calculate each active power of the power
transmitting/receiving direction Pna2, Pnb2, Pnc2 caused by the
reverse load flow by using voltage and phase difference per phase
and a 1/3 current value of neutral line current since the neutral
line current (In m) becomes 3 times higher than zero-sequence (is
0). The reverse load flow active power of the power transmitting
direction may be obtained by the active power calculating functions
of Equation 27 to Equation 29:
Pna2=Va.sub.--m*In.sub.--m*cos .theta.na2/3 Equation 27
[0159] (wherein, Pna2 is active power of a phase during the reverse
load flow, Va_m is voltage of a phase, In_m is neutral line
current, .theta.na2 is phase difference during the reverse load
flow)
Pnb2=Vb.sub.--m*In.sub.--m*cos .theta.nb2/3 Equation 28
[0160] (wherein, Pnb2 is active power of b phase during the reverse
load flow, Vb_m is voltage of b phase, In_m is neutral line
current, .theta.nb2 is active power of b phase during the reverse
load flow)
Pnc2=Vc.sub.--m*In.sub.--m*cos .theta.nc2/3 Equation 29
[0161] (wherein, Pnc2 is active power of c phase during the reverse
load flow, Vc_m is voltage of c phase, In_m is neutral line
current, .theta.nc2 is phase difference of c phase during the
reverse load flow)
[0162] Reactive power of the reverse load flow is calculated at the
reactive reverse load flow power per phase calculating unit 662 as
in FIG. 35 which calculates reactive power of the reverse load flow
of the power transmitting direction Qna2, Qnb2, Qnc2 by using
voltage per phase and phase difference of the neutral line current
by the same calculation method which the active power calculating
unit of the reverse load flow 661 calculates.
[0163] Here, the reactive reverse load flow calculating unit 662
may calculate reactive reverse load flow per phase by using
Equation 30 to Equation 32:
Qna2=Va.sub.--m *In.sub.--m*sin .theta.na2/3 Equation 30
[0164] (wherein, Qna2 is reactive power of a phase during the
reverse load flow, Va_m is voltage of a phase, In_m is neutral line
current, .theta.na2 is phase difference during the reverse load
flow)
Qnb2=Vb.sub.--m*In.sub.--m*sin .theta.nb2/3 Equation 31
[0165] (wherein, Qnb2 is reactive power of b phase during the
reverse load flow, Vb_m is voltage of b phase, In_m is neutral line
current, .theta.nb2 is phase difference of b phase during the
reverse load flow)
Qnc2=Vc.sub.--m*In.sub.--m*sin .theta.nc2/3 Equation 32
[0166] (wherein, Qnc2 is reactive power of c phase during the
reverse load flow, Vc_m is voltage of c phase, In_m is neutral line
current, .theta.nc2 is phase difference of c phase during the
reverse load flow)
[0167] Here, the reverse load flow determining unit 64 may
determine whether a reverse load flow occurs or not by comparing
the intensity of load current per phase when a reverse load flow
occurs with that of the neutral line current in a system. Because
multiple functions 653, 656 multiple 1 to a rev value when a
reverse load flow occurs, while they do 0 when a reverse load flow
does not occur to determine whether to compensate active, reactive
power caused by the a reverse load flow, the reverse load flow
determining unit 64 is thus able to determine whether to compensate
active power and reactive power according to the occurrence of the
reverse load flow.
[0168] The power transmitting direction reverse load flow
calculating unit 68 can determine whether or not the active power
and the reactive power generated by the reverse load flow are to be
compensated. Here, in order to determine the compensation of the
active power and the reactive power, the power transmitting
direction reverse load flow calculating unit 68 multiplies 1 to the
reverse value when there is reverse load flow and multiplies 0 to
the reverse value when there is no reverse load flow.
[0169] A power transmitting actual power usage calculating unit 68
may calculate actual power usage by employing the instantaneous
power value inputted from the power transmitting instantaneous
power calculating unit 63 and the reverse load flow power value
inputted from the power transmitting reverse load flow calculating
unit 66.
[0170] For this purpose, the power transmitting actual power usage
calculating unit 68 may include a power transmitting instantaneous
compensation active power per phase calculating unit 681, a power
receiving instantaneous compensation reactive power per phase
calculating unit 682, a 3 phase power transmitting instantaneous
compensation active power per phase calculating unit 683, and a 3
phase power transmitting instantaneous compensation reactive power
per phase calculating unit 684.
[0171] As shown FIG. 36 to FIG. 40, the power transmitting
instantaneous compensation active power per phase calculating unit
681 may calculate each out value Pa20, Pb20, Pc20 of compensated
instantaneous active power per phase traded between a provider and
a user by subtracting reverse load flow instantaneous active power
per phase, Pna2, Pnb2, Pnc2 from power transmitting instantaneous
active power per phase, Pa2, Pb2, Pc2.
[0172] The power transmitting instantaneous compensation reactive
power per phase calculating unit 682 may calculate each out value
Qa20, Qb20, Qc20 of compensated instantaneous reactive power per
phase traded between a provider and a user by subtracting reverse
load flow instantaneous reactive power per phase, Qna2, Qnb2, Qnc2
from power transmitting instantaneous reactive power per phase Qa2,
Qb2, Qc2.
[0173] The 3 phase power receiving transmitting instantaneous
compensation active power calculating unit 683 may calculate 3
phase power transmitting instantaneous compensation active power
P34_20 by conducting vector sum of instantaneous power per phase
Pa20, Pb20, Pc20 compensated at the same point per phase with a 3
terminal addition function to determine 3 phase active power.
[0174] Further, the 3 phase power transmitting instantaneous
compensation reactive power calculating unit 684 may calculate 3
phase power transmitting instantaneous compensation reactive power
Q34_20 by conducting vector sum of reactive power per phase Qa20,
Qb20, Qc20 compensated at the same point per phase with a 3
terminal addition function to determine 3 phase reactive power of
the power transmitting direction.
[0175] A power transmitting direction determining unit 70 may
determine power receiving direction un-metered usage, active power
and reactive power from the calculated actual power usage value to
store actual power usage value.
[0176] As shown in FIG. 41, the power transmitting direction
determining unit 70 may include a power transmitting active power
determining unit 72 and a power transmitting reactive power
determining unit 74.
[0177] As shown in FIG. 42, the power transmitting active power
determining unit 72 may determine 0 if the value Pa20, Pb20, Pc20,
P34_20 of active power compensated from intensity selecting unit
712 is equal to or smaller than 0 and determine active power value
if it is higher than 0.
[0178] As shown in FIG. 42 and FIG. 43, the power transmitting
reactive power determining unit 74 may determine active power of
the power transmitting direction and determine reactive power value
Qa20, Qb20, Qc20, Q34_20 if active power value Pa20, Pb20, Pc20,
P34_20 compensated at the intensity selecting unit 712 is higher
than 0, and output 0 for a reactive power value at the multiple
function 653 if active power value Pa20, Pb20, Pc20, P3420 is
smaller than 0.
[0179] In addition, reverse direction load flow per phase of the
power transmitting direction is detected and out value DRA, DRB,
DRC is outputted when the sum of 3 phase active power of the power
transmitting direction is smaller than 0 and the instantaneous
active power per phase of the power transmitting direction is
higher than 0.
[0180] Further, when 3 phase active power of the power transmitting
direction P34_20 is higher than 0, an out value P34R is outputted
as 1 and when 3 phase active power of the power transmitting,
receiving direction is equal to or smaller than 0, 0 is
outputted.
[0181] The power transmitting reactive power determining unit 74
may divide the outputted reactive power to lagging reactive power
and leading reactive power. As shown in FIG. 44, the intensity
selecting unit 712 selects lagging reactive power Qa21, Qb21, Qc21,
3Q21 if the compensated reactive power per phase and the
compensated reactive power of 3 phase of the power transmitting
direction Qa20, Qb20, Qc20, Q34_20 are higher than 0, and selects
leading reactive power Qa22, Qb22, Qc22, 3Q22 if they are smaller
than 0.
[0182] The power transmitting direction active power storing unit
78 illustrated in FIG. 45 performs the same function which the
power receiving direction active power storing unit 75 does. The
power receiving direction lagging reactive power storing unit 76
illustrated in FIG. 46 performs the same function which the power
transmitting direction lagging reactive power storing unit 79 does.
The power transmitting direction leading reactive power storing
unit 80 illustrated in FIG. 47 performs the same function which the
power receiving direction leading reactive power storing unit 77
does. Therefore, the overlapped description is omitted.
[0183] A power transmitting apparent power/power factor calculating
unit 82 may calculate apparent power and power factor and outputs
the results. As shown in FIG. 48, the power transmitting apparent
power/power factor calculating unit 82 may include a power
transmitting apparent power calculating unit 821 and a power factor
calculating unit 822, respectively.
[0184] For example, as shown in FIG. 49, the power transmitting
apparent power calculating unit 821 may calculate apparent power
per phase and 3 phase power transmitting apparent power. Here, the
power transmitting apparent power calculating unit 821 may
calculate each apparent power per phase and amount of apparent
power 2Sa, 2Sb, 2Sc, 3S2 by employing functions for calculating
apparent power of Equation 33 to Equation 36 by using power
transmitting RSM value-treated active power active power, lagging
reactive power, leading reactive power and accumulated usage.
2Sa= {square root over
(Pa20.sub.kwh.sup.2+(Qa21.sub.kvarh+Qa22.sub.kvarh).sup.2)}
Equation 33
[0185] (wherein, Pa20 is active power of a phase, Qa21 is lagging
active power of a phase, Qa22 is leading reactive power of a
phase)
2Sb= {square root over
(P20.sub.kwh.sup.2+(Qb21.sub.kvarh+Qb22.sub.kvarh).sup.2)} Equation
34
[0186] (wherein, Pa20 is active power of b phase, Qa21 is lagging
reactive power of b phase, Qa22 is leading reactive power of b
phase)
2Sc= {square root over
(Pc20.sub.kwh.sup.2+(Qc21.sub.kvarh+Qc22.sub.kvarh).sup.2)}
Equation 35
[0187] (wherein, Pc20 is active power of c phase, Qc21 is lagging
reactive power of c phase, Qc22 is leading reactive power of c
phase)
3S2= {square root over
(3P20.sub.kwh.sup.2+(3Q21.sub.kvarh+3Q22.sub.kvarh).sup.2)}
Equation 36
[0188] As shown in FIG. 50, the power transmitting power factor
calculating unit 822 may calculate power transmitting power factor
per phase and 3 phase power transmitting power factor by employing
power factor calculating functions with using power transmitting
active power and usage Pa20_kwh, Pb20_kwh, Pc20_kwh, 3P20_kwh and
apparent power and apparent power usage 2Sa, 2Sb, 2Sc, 3S2.
[0189] Equation 37 to Equation 40 are equations for power
transmitting power factors and 3 phase power transmitting power
factors of a, b, and c phase.
A cos .theta.20=Pa20_kwh/2Sa Equation 37
B cos .theta.20=Pb20_kwh/2Sb Equation 38
C cos .theta.20=Pc20_kwh/2Sc Equation 39
3 cos .theta.20=3P20_kwh/3S2 Equation 40
[0190] An active power zone which is power receiving reverse load
flow compensated per phase according to an embodiment of the
present invention has a single phase bidirectional calculating zone
unlike a conventional one way type so that it allows calculating
and compensating an intensity of reverse load flow per phase
according to phase angle direction of reverse load flow per phase
in real time and determining only actually used active power when
reverse load flow occurs by a power system.
[0191] Particularly, since reactive power unlike active power has
to determine lagging power and leading power during receiving power
and transmitting power with a phase angle of 180.degree., an error
in amount of reactive power may be severely caused according to
phase when reverse load flow occurs.
[0192] A reactive power zone which is reverse load flow compensated
per phase for receiving power compensates the same way as the
active power compensation. Reactive power per phase is calculated
and the result is compensated to actually used reactive power when
reverse load flow occurs.
[0193] A calculating zone which is reverse load flow compensated
for receiving power per phase may have a single phase bidirectional
calculating zone type using 1, 2, 3, 4 quadrants unlike a
conventional one way type using 1, 4 quadrants.
[0194] A 3 phase power calculating zone performs a 3 phase vector
addition of instantaneous power compensated per phase. For example,
a guideline for receiving power, which is reverse load flow
compensated, compensates power actually used by a user per phase
and determines the used amount even though phase angle per phase
changes when reverse load flow occurs. Contrary to this, a
guideline for transmitting power, which is reverse load flow
compensated, does not determine the used amount in the direction of
reverse load flow. A power receiving power meter and a power
transmitting power meter, use identical calculation algorithm and a
bidirectional power meter may be a one body combining the power
receiving power meter and the power transmitting power meter.
[0195] FIG. 51 is a flow chart illustrating a method for metering
by a 3 phase bidirectional system for compensating reverse load
flow according to an embodiment of the present invention.
[0196] According to FIG. 51, a metering method by using a 3 phase
bidirectional system for compensating reverse load flow according
to an embodiment of the present invention may include: detecting
voltage/current per phase (S10), determining neutral line current
and phase difference per phase of the power transmitting/receiving
direction (S20), determining reverse load flow (S30), calculating
instantaneous power (S50), calculating reverse load flow (S40),
calculating actual power usage (S60), determining active power
(S70), determining reactive power (S80), measuring and storing
amount of active power (S90), measuring and storing amount of
lagging reactive power (S100), measuring and storing amount of
leading reactive power (S110), and calculating apparent power or
power factor (S120).
[0197] Voltage per phase or current per phase may be detected by
using voltage value and current value inputted from a sensor (S10).
Here, the sensor may include an instrument transformer and a
current transformer.
[0198] Here, the detected voltage and current per phase may be
converted to a discrete signal by sampling and the voltage and
current per phase converted to a discrete signal may be further
converted by the fast Fourier transform to divide to intensity per
degree, phase per degree and DC component to calculate
non-sinusoidal wave power.
[0199] The detected voltage value and current value is then used to
determine neutral line current and each phase difference per phase
of the power transmitting/receiving direction to determine power
receiving direction and power transmitting direction (S20). Here,
the power receiving direction may be determined by subtracting the
phase of current per phase from the phase of voltage per phase and
the power transmitting direction may be determined by adding
180.degree. to the determined power receiving direction.
[0200] A neutral line current may be determined by calculating 3
phase current vector sum and may be determined by one chosen from
the following methods: (i) dividing 3 phase current into a
positive-sequence, a negative-sequence and a zero-sequence using
the method of symmetrical coordinates; (ii) indirectly determining
3 phase current inside the power meter; and (iii) directly
determining current of primary neutral line of an interconnection
transformer.
[0201] Reverse load flow may be then determined by using the
determined each phase difference per phase and neutral line current
(S30). Here, if the intensity of zero-sequence is higher than that
of negative-sequence by comparing the intensity of a fundamental
component of negative-sequence and that of zero-sequence, 1 may be
outputted, while 0 may be outputted if it is equal to or smaller.
When 1 is outputted, it may be determined as occurrence of reverse
load flow and when 0 is outputted, it may be determined as no
occurrence of reverse load flow
[0202] When reverse load flow occurs during the determining reverse
load flow, reverse load flow power may be calculated (S40). Here,
each of active power and reactive power of reverse load flow power
is calculated. Here, each of active power and reactive power of
reverse load flow of power receiving direction or power
transmitting direction is calculated.
[0203] Instantaneous power may be calculated after determining
bidirection (S50). Instantaneous power may be calculated by
employing an instantaneous power calculating function using each
current and phase difference per phase. Instantaneous power may be
calculated by dividing into instantaneous active power and
instantaneous reactive power. Instantaneous power may be calculated
by employing Equations 1 to 12.
[0204] Actual power usage may be then calculated by calculating
instantaneous compensation power per phase and 3 phase
instantaneous compensation power using the instantaneous power and
the reverse load flow power (S60). Here, compensated instantaneous
power per phase and compensated 3 phase instantaneous power may be
calculated at the direction selected from power receiving direction
and power transmitting direction.
[0205] Here, each out value of power receiving compensated
instantaneous active power per phase actually traded between a
provider and a user may be calculated by using each function
subtracting the reverse load flow instantaneous active power per
phase from the power receiving instantaneous active power per
phase.
[0206] For example, each out value of power receiving compensated
instantaneous reactive power per phase actually traded between a
provider and a user may be calculated by using each function
subtracting the reverse load flow instantaneous reactive power per
phase from the power receiving instantaneous reactive power per
phase.
[0207] 3 Phase power receiving instantaneous compensation active
power may be calculated by performing vector addition of
instantaneous power per phase compensated at the same point with a
3 terminal addition function to determine 3 phase active power.
Further, 3 phase power receiving instantaneous compensation
reactive power may be calculated by performing vector addition of
reactive power per phase compensated at the same point with a 3
terminal addition function to determine 3 phase reactive power.
[0208] Power transmitting instantaneous active power, power
transmitting instantaneous reactive power, and power transmitting 3
phase instantaneous power may be also calculated by the same
method.
[0209] Active power of actual power usage may be then determined
(S70). When active power of actual power usage is determined,
instantaneous power per phase divided into the intensity and phase
for each degree and DC component by employing the fast Fourier
transform is added at the same point and then if the 3 phase added
value is higher than 0, power per phase and 3 phase power is
calculated by accumulating to the forward direction (power
receiving). If the 3 phase added value is smaller than 0, power per
phase and 3 phase power is calculated by accumulating to the
reverse direction (power transmitting).
[0210] Reactive power of actual power usage may be then determined
(S80). When active power of actual power usage is determined,
reactive power per phase compensated at the same point per phase
may be added. Here, if the outputted reactive power may be divided
into lagging reactive power and leading reactive power. For
example, if the power receiving direction compensated reactive
power per phase and 3 phase reactive power is higher than 0, it
selects lagging reactive power, while if it is smaller than 0, it
selects leading reactive power. Power transmitting direction also
uses the same method.
[0211] Power amount of active power or reactive power is measured
according to the active power or the reactive power and stored the
result (S90, S100, S110). Here, the reactive power may measure
amount of lagging reactive power and amount of leading reactive
power. Further, each amount of active power or reactive power for
the power receiving direction or the power transmitting direction
may be measured and stored. The power amount may be accumulated
with time.
[0212] Apparent power or power factor is calculated by using the
measured amount of active power or reactive power (S120). Apparent
power may be calculated by employing Equation 19 to Equation 22 or
Equation 33 to Equation 36 and power factor be calculated by
employing Equation 19 to Equation 22 or Equation 23 to Equation 26
or Equation 37 to 40.
[0213] While it has been described with reference to particular
embodiments, it is to be appreciated that various changes and
modifications may be made by those skilled in the art without
departing from the spirit and scope of the embodiment herein, as
defined by the appended claims and their equivalents. [0214] 60:
voltage per phase and current detecting unit [0215] 61:
bidirectional measuring unit [0216] 62: power receiving
instantaneous power calculating unit [0217] 63: power transmitting
instantaneous power calculating unit [0218] 64: reverse load flow
determining unit [0219] 65: power receiving reverse load flow
calculating unit [0220] 66: power transmitting reverse load flow
calculating unit [0221] 67: power receiving actual power usage
calculating unit [0222] 68: power transmitting actual power usage
calculating unit [0223] 69: power receiving direction selecting
unit [0224] 70: power transmitting direction selecting unit [0225]
71: power receiving active power determining unit [0226] 72: power
transmitting active power determining unit [0227] 73: power
receiving reactive power determining unit [0228] 74: power
transmitting reactive power determining unit [0229] 75: power
receiving active power and usage [0230] 76: power receiving lagging
reactive power and usage [0231] 77: power receiving leading
reactive power and usage [0232] 78: power transmitting active power
and usage [0233] 79: power transmitting lagging reactive power and
usage [0234] 80: power transmitting leading reactive power and
usage [0235] 81: power receiving apparent power and power factor
calculating unit [0236] 82: power transmitting apparent power and
power factor calculating unit
* * * * *